This invention relates to a device for transmitting large forces between a superconducting magnet winding cooled to a very low temperature and an abutment which is at a higher temperature level and takes up the forces.
A device for transmitting large forces from a super conducting magnet winding forming an energy storage device, the supports of which contain several support members which are arranged one behind the other in the direction of the force transmission and are thermally divided by a metal sheet serving as a heat shield, is described, for instance, in U.S. Pat. No. 3,980,981.
Such force transmission devices are required particularly for inductive superconducting energy storage devices. The great advantage of such storage devices is seen in the fact that with them, energies in the order of 10.sup.12 joule or more can be stored in a relatively small volume, and energy densities of about 10 joule/cm.sup.3 can be obtained with magnetic flux densities of about 5 tesla or more. Such high flux densities can be produced in magnet windings economically only by means of so-called technical Type II superconductors such as niobium-titanium (Nb-Ti), niobium-tin (Nb.sub.3 Sn) or vandium-gallium (V.sub.3 Ga). Similar energy storage devices generally contain a number of coaxial solenoids of these conductors into which the electric energy is fed during low load periods of many hours via an inverter from a connected power supply network. During peak load times, the required energy can then be given off to the network again over a period of minutes or hours.
In accordance with one proposal for a corresponding superconducting energy storage device, with which supposedly several gigawatt hours can be stored, three magnet windings of stabilized niobium-titanium superconductors are provided. Each of the windings should have a diameter of between 120 and 150 m, and is 5 m wide and 8 to 10 m high. They are to be fabricated in situ in tunnels which are driven into the rock ("IEE Transactions on Magnetics", vol. MAG 11, no. 2, March 1975, pages 475 to 488).
The forces emanating from the superconducting winding of such a gigawatt magnetic storage device, such as Lorentz forces, are, for instance, on the order of magnitude of 10.sup.11 newton. It must be possible to safely transmit these very large forces using a force transmission device between the superconducting magnet winding and an outer abutment which takes up the force and for which, especially for cost reasons, natural rock is provided. In addition, it is a prime requirement for such a force transmission device that the thermal losses due to solid body heat inflow through it into the windings which are at a very low temperature be kept as low as possible. For, the economic feasibility of a superconducting energy storage device is determined in particular also by these heat losses.
These requirements are supposedly also met by the force transmitting device described in U.S. Pat. No. 3,980,981. According to one embodiment, this device contains columnar supports which extend radially outward with respect to the axis of a superconducting magnet winding associated therewith approximately in the direction of the force transmission. These supports are furthermore mutually guyed so as to ensure sufficient strength (FIG. 1). Also, pairs of supports engage, at their end facing the magnet winding, a common support point so that they represent the two legs of an A shaped support arrangement. These supports are furthermore held in a firm mutual position by stiffening elements extending transversely to the bracing direction (FIG. 3.) In the known force transmission devices also provided, approximately concentrically about the magnet winding, are sheet-like thermal radiation shields which consist of metallic surfaces and superinsulation. These shields subdivide the supports thermally in the direction of the force transmission.
It has been found, however, that these known force transmitting devices, especially also those with an A shaped support have only relatively little buckling strength. In order to prevent buckling of the support under load, the supports of the known force transmission devices must therefore have a sufficiently large material cross section. This, however, leads to correspondingly large losses due to heat inflow to the parts cooled to the lowest temperature of the storage device and therefore, to a reduction of its efficiency.
It is therefore an object of the present invention to develop a force transmission device of the type mentioned at the outset in such a manner that with it, the large forces occurring in a superconducting energy storage device can be safely transmitted to the outside, and the thermal losses due to solid body heat inflow via its support cross section are nevertheless relatively small.